As a Clinical Center in the new Pediatric Heart Disease Clinical Research Network (PHDCRN), the Children?s Hospital of Philadelphia (CHOP) will participate collaboratively with the Network to improve outcomes for children with heart disease, provide an evidential base for therapies currently used or considered, develop new therapies, and disseminate that information to the medical community. To achieve this goal, we will address the following aims: Aim 1: Develop an infrastructure and investigational team for to assure full participation in PHDCRN; Aim 2: Develop procedures and policies to assure proper implementation of approved PHDCRN protocols; Aim 3: Fully participate in the development new protocols and dissemination of information to the scientific community. Two protocols are proposed for the PHDCRN?s scientific agenda that emphasize the research strengths of the Cardiology Division, the Cardiac Center and CHOP. The short-term study investigates the use of biventricular pacing or cardiac resynchronization in children with severe congestive heart failure and dilated cardiomyopathy. The primary aim of the study is to evaluate the acute effects of biventricular pacing on cardiac function as measured by oxygen consumption during exercise in a 6-week randomized controlled clinical trial. After the 6-week randomized comparison, all patients are paced and longer-term effects on cardiac function, functional capacity and quality of life will be evaluated out to 12 months. The long-term project investigates whether enalapril (ACE inhibition) can reduce the time-related decline in exercise performance experienced by patients with single ventricle who have undergone the Fontan procedure. The primary aim will be to evaluate the effects of ACE inhibition over a 4-year period on maximal oxygen consumption measured during exercise testing in a double blinded randomized clinical trial design. The Children?s Hospital of Philadelphia Cardiology Division and Cardiac Center has a distinguished history of clinical innovation and excellence in cardiac care, a high volume program with expertise in all areas of pediatric cardiology including cardiac arrhythmias, echocardiography, exercise physiology catheterization including interventions, intensive care, cardiac magnetic resonance imaging, transplantation, and surgery for heart disease. Patient care is integrated through a multidisciplinary Cardiac Center. The faculty of the Cardiac Center are experienced investigators and maintain a highly productive program of multicenter and institutional clinical trials and studies. CHOP has made major investments in the clinical research infrastructure that support essential functions in clinical investigations. These programmatic and institutional strengths support the aims and enhance the likelihood that the long-term goals of the PHDCRN will be achieved.